1 Field of the Invention
The present invention relates to a packaged semiconductor substrate, and more particularly to a degatable electrically insulating layer provided between the position for pouring the package encapsulant and the substrate to prevent direct contact between the package encapsulant and the substrate surface at the position for pouring the package encapsulant during manufacture of a substrate for a ball grid array integrated circuit (BGA IC).
2. Description of the Related Art
Conventional quad flat pack (QFP) and pin-grid array (PGA) methods for packaging integrated circuits cannot meet practical needs as the functions of integrated circuits have become more and more complicated while the integration level of the circuits become higher and higher. Ball grid array integrated circuit (BGA IC) packaging method is one of the newly developed methods for ICs with a quantity of pins and is suitable for packaging ultra-large scale integration (ULSI) produced by submicron solution.
Referring to FIG. 1A, when proceeding with plastic BGA packaging that is common in BGA ICs, a mold (not shown) is put on top of the substrate 11 of a BGA IC (an electronic device 10 to be packaged), and molten liquid plastic material (i.e., a package encapsulant) is then poured into the mold to completely enclose the integrated circuits on the substrate 11 to thereby provide a completely air tight seal for the integrated circuit chips. Referring to FIG. 1B, the BGA IC (the packaged electronic device 10) is removed from the mold after the plastic material is hardened. Subsequent trim work is carried out on an area adjacent a mold gate (not shown) of the mold to remove the residual plastic material in a pouring channel (not shown) of the mold. In the above-mentioned packaging method for BGA ICs, a metallic plate 13 (FIG. 2) is provided on the substrate 11 and includes a metallic surface formed by depositing gold on a side thereof. When the substrate is covered by the mold, the metallic surface is located below the pouring channel of the mold. The metallic surface serves as an isolating layer between the substrate and the pouring channel during pouring of the package encapsulant, thereby providing an increased degating ability. More specifically, when removing the substrate from the mold, the metallic surface allows the residual package encapsulant in the pouring channel to be easily degated from the substrate. Thus, the residual on the packaged IC can be easily trimmed. Nevertheless, in addition to an increased cost as a result of using gold, the metallic plate occupies a certain space and thus reduces the space available for layout. Furthermore, as shown in FIG. 2, when the metallic plate 13 is expanded as a result of heat, the solder masks 15 on both sides of the metallic plate 13 are squeezed in the lateral direction such that the layout 14 in each solder mask 15 is also squeezed. As a result, the product defective index is increased.